(1) Field of the Invention
The present invention relates generally to a self-locking mechanism for a gear set, and more particularly to an automatic locking device that substantially prevents a gear set from being back-driven while permitting the gear set to be forward-driven.
(2) Background Information
The use of gear sets (two or more gears meshed together) is well known for a wide variety of applications and in a wide range of devices. Typically, when two or more gears of any type (e.g., helical, worm) are meshed with one another, each gear in the chain is capable of driving the others in either rotational direction (i.e., clockwise or counterclockwise). Depending upon the frictional forces inherent in the gear set, system forces acting on the resting gears may at times cause unwanted movement thereof (in either a clockwise or counterclockwise direction). For example, when positioning a butterfly valve in a fluid stream, the fluid""s dynamic forces may become greater than the friction in the gear set and/or the power supply, thus moving the butterfly valve out of position and causing it to back-drive the gear set. For many applications, such back driving is undesirable.
Therefore, there exists a need for a self-locking apparatus for a gear set. In particular there exists a need for a locking apparatus that automatically locks a gear set, preventing the gear set from being back-driven, yet permitting it to be efficiently forward-driven, e.g., by a power source.
One aspect of the present invention includes a self-locking device for a gear set configured for being forward-driven at an input in either of first and second rotational directions and for substantially preventing an output from being back-driven in either of the rotational directions. The device includes an input including a drive shaft configured for being forward-driven in either of the first and second rotational directions and an output including a gear disposed to rotate with the drive shaft. The device further includes first and second releasable couplings coupled to the gear and first and second ratchets respectively coupled to the first and second releasable couplings. The first ratchet is disposed to substantially prevent rotation in the first direction and to permit rotation in the second direction, and the second ratchet is disposed to substantially prevent rotation in the second direction and permit rotation in the first direction. The first releasable coupling is disposed to selectively couple and decouple the gear with the first ratchet, and the second releasable coupling is disposed to selectively couple and decouple the gear with the second ratchet. The releasable couplings are configured to automatically, selectively engage and disengage the ratchets with the gear, the selective engaging and disengaging permitting the input to be said forward-driven in either of the rotational directions and substantially preventing the output from being said back-driven in either of the rotational directions. In one variation of this aspect, a worm gear is disposed between first and second ratchet cams. First and second friction couplings, e.g., friction plates, are interposed respectively between the first ratchet cam and the worm gear and the second ratchet cam and the worm gear.
In another aspect, this invention includes a gearbox. The gearbox includes a gear set including a gear meshed with a wheel, the gear being disposed to rotate with a drive shaft. First and second releasable couplings are coupled to the gear. First and second ratchets are respectively coupled to the first and second releasable couplings. The first ratchet is disposed to substantially prevent rotation in a first direction and to permit rotation in a second direction, and the second ratchet is disposed to substantially prevent rotation in the second direction and to permit rotation in the first direction. The first releasable coupling is disposed to selectively couple and decouple the gear with the first ratchet, and the second releasable coupling is disposed to selectively couple and decouple the gear with the second ratchet. The releasable couplings are configured to automatically, selectively engage and disengage the ratchets with the gear, the selective engaging and disengaging permitting the input to be forward-driven in either of the rotational directions and substantially preventing the output from being back-driven in either of the rotational directions. A method for fabricating a gearbox is also provided.